EmptySet：iOS列表占位处理

描述：

列表没有数据、无网络状态下显示占位图处理

场景：

列表没有数据、无网络状态

原理：

捕捉UITableView/UICollectionView的reloadData事件，判断列表有无数据，处理展示占位图逻辑

介绍：

1. EmpySet使用分类UIScrollView+CYEmptySet实现
2. 对无任何侵入性，不依赖于任何三方库

使用：

Paste_Image.png

Demo展示：

CYEmptySet.gif

部分代码：

static char CYEmptySetCustomViewKey;

static char CYEmptySetContentViewKey;

static char CYEmptySetEmptyEnabledKey;

@interface UIScrollView ()

@property (nonatomic, weak) UIView *contentView;

@end

@implementation UIScrollView (CYEmptySet)

- (void)exchangeSeletor1:(SEL)selector1 selector2:(SEL)selector2 {
    Class class = [self class];
    Method originalMethod = class_getInstanceMethod(class, selector1);
    Method swizzledMethod = class_getInstanceMethod(class, selector2);
    
    // Change implementation
    BOOL success = class_addMethod(class, selector1, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    if (success) {
        class_replaceMethod(class, selector2, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

- (void)setContentView:(UIView *)contentView {
    objc_setAssociatedObject(self, &CYEmptySetContentViewKey, contentView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (UIView *)contentView {
    UIView *contentView = objc_getAssociatedObject(self, &CYEmptySetContentViewKey);
    if (!contentView) {
        contentView = [UIView new];
        contentView.backgroundColor = [UIColor clearColor];
        self.contentView = contentView;
    }
    contentView.translatesAutoresizingMaskIntoConstraints = false;
    return contentView;
}

- (void)cy_reloadData {
    [self cy_reloadData];
    
    if (!self.emptyEnabled) return;
    UIView *contentView = self.contentView;
    
    if ([self rowCount] == 0) {
        if (([self isKindOfClass:[UITableView class]] || [self isKindOfClass:[UICollectionView class]])
            && !contentView.superview
            && self.subviews.count > 1) {
            [self addSubview:contentView];
            [self insertSubview:contentView atIndex:0];
            if (self.customEmptyView) {
                self.customEmptyView.translatesAutoresizingMaskIntoConstraints = false;
                [contentView addSubview:self.customEmptyView];
            }
            [self addConstraint:[NSLayoutConstraint constraintWithItem:self.contentView
                                                             attribute:NSLayoutAttributeWidth
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:self
                                                             attribute:NSLayoutAttributeWidth
                                                            multiplier:1.0
                                                              constant:0.0]];
            
            [self addConstraint:[NSLayoutConstraint constraintWithItem:self.contentView
                                                             attribute:NSLayoutAttributeHeight
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:self
                                                             attribute:NSLayoutAttributeHeight
                                                            multiplier:1.0
                                                              constant:0.0]];
            
            [self addConstraintWithLayoutAttributes:@[@(NSLayoutAttributeLeft),
                                                      @(NSLayoutAttributeBottom),
                                                      @(NSLayoutAttributeRight)] view:self.contentView equalToSuperView:self];
            [self addConstraint:[NSLayoutConstraint constraintWithItem:self.contentView
                                                             attribute:NSLayoutAttributeTop
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:self
                                                             attribute:NSLayoutAttributeTop
                                                            multiplier:1.0 constant:-self.contentInset.top]];
            [self addConstraintWithLayoutAttributes:@[@(NSLayoutAttributeTop),
                                                      @(NSLayoutAttributeLeft),
                                                      @(NSLayoutAttributeBottom),
                                                      @(NSLayoutAttributeRight)] view:self.customEmptyView equalToSuperView:self.contentView];
            
            
            
        }
    } else {
        [contentView.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];
        [contentView removeFromSuperview];
        self.contentView = nil;
    }
    
}

- (void)addConstraintWithLayoutAttributes:(NSArray *)attributes view:(UIView *)view equalToSuperView:(UIView *)superView {
    if (!superView || !view) return;
    for (NSNumber *attribute in attributes) {
        NSLayoutAttribute att = attribute.integerValue;
        NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:view
                                                                      attribute:att
                                                                      relatedBy:NSLayoutRelationEqual
                                                                         toItem:superView
                                                                      attribute:att
                                                                     multiplier:1.0
                                                                       constant:0.0];
        [superView addConstraint:constraint];
    }
}

- (NSInteger)rowCount {
    NSInteger rowCount = 0;
    if ([self isKindOfClass:[UITableView class]]) {
        UITableView *tableView = (UITableView *)self;
        for (NSInteger section = 0; section < tableView.numberOfSections; section++) {
            rowCount += [tableView numberOfRowsInSection:section];
        }
    } else if ([self isKindOfClass:[UICollectionView class]]) {
        UICollectionView *collectionView = (UICollectionView *)self;
        for (NSInteger section = 0; section < collectionView.numberOfSections; section++) {
            rowCount += [collectionView numberOfItemsInSection:section];
        }
    }
    return rowCount;
}

- (UIView *)customEmptyView {
    return objc_getAssociatedObject(self, &CYEmptySetCustomViewKey);
}

- (void)setCustomEmptyView:(UIView *)customEmptyView {
    objc_setAssociatedObject(self, &CYEmptySetCustomViewKey, customEmptyView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (BOOL)emptyEnabled {
    return [objc_getAssociatedObject(self, &CYEmptySetEmptyEnabledKey) boolValue];
}

- (void)setEmptyEnabled:(BOOL)emptyEnabled {
    if (emptyEnabled) {
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            [self exchangeSeletor1:@selector(reloadData) selector2:@selector(cy_reloadData)];
        });
    }
    objc_setAssociatedObject(self, &CYEmptySetEmptyEnabledKey, @(emptyEnabled), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

Demo和代码下载地址：Demo和代码下载地址